This tutorial is Copyright (c) 2014 by Falko Timme & Srijan Kishore. It is derived from a tutorial from Christoph Haas which you can find at http://workaround.org. You are free to use this tutorial under the Creative Commons license 2.5 or any later version.

This document describes how to install a Postfix mail server that is based on virtual users and domains, i.e. users and domains that are in a MySQL database. I'll also demonstrate the installation and configuration of Courier (Courier-POP3, Courier-IMAP), so that Courier can authenticate against the same MySQL database Postfix uses.

The resulting Postfix server is capable of SMTP-AUTH and TLS and quota (quota is not built into Postfix by default, I'll show how to patch your Postfix appropriately). Passwords are stored in encrypted form in the database (most documents I found were dealing with plain text passwords which is a security risk). In addition to that, this tutorial covers the installation of Amavisd, SpamAssassin and ClamAV so that emails will be scanned for spam and viruses. I will also show how to install SquirrelMail as a webmail interface so that users can read and send emails and change their passwords.

The advantage of such a "virtual" setup (virtual users and domains in a MySQL database) is that it is far more performant than a setup that is based on "real" system users. With this virtual setup your mail server can handle thousands of domains and users. Besides, it is easier to administrate because you only have to deal with the MySQL database when you add new users/domains or edit existing ones. No more postmap commands to create db files, no more reloading of Postfix, etc. For the administration of the MySQL database you can use web based tools like phpMyAdmin which will also be installed in this howto. The third advantage is that users have an email address as user name (instead of a user name + an email address) which is easier to understand and keep in mind.

This howto is meant as a practical guide; it does not cover the theoretical backgrounds. They are treated in a lot of other documents in the web.

This document comes without warranty of any kind! I want to say that this is not the only way of setting up such a system. There are many ways of achieving this goal but this is the way I take. I do not issue any guarantee that this will work for you!

1 Preliminary Note

This tutorial is based on Ubuntu 13.10 Server (Saucy Salamander), so you should set up a basic Ubuntu 13.10 server installation before you continue with this tutorial. The system should have a static IP address. I use 192.168.0.100 as my IP address in this tutorial and server1.example.com as the hostname.

Make sure that you are logged in as root (type in

sudo su

to become root), because we must run all the steps from this tutorial as root user.

Pick the postfix and postfix-mysql packages and install them like this:

dpkg -i postfix_2.10.2-1_amd64.deb postfix-mysql_2.10.2-1_amd64.deb

4 Create The MySQL Database For Postfix/Courier

Now we create a database called mail:

mysqladmin -u root -p create mail

You will be asked for this question:

Enter Password:<-- yourrootsqlpassword

Next, we go to the MySQL shell:

mysql -u root -p

On the MySQL shell, we create the user mail_admin with the passwort mail_admin_password (replace it with your own password) who has SELECT,INSERT,UPDATE,DELETE privileges on the mail database. This user will be used by Postfix and Courier to connect to the mail database:

The users table stores all virtual users (i.e. email addresses, because the email address and user name is the same) and passwords (in encrypted form!) and a quota value for each mail box (in this example the default value is 10485760 bytes which means 10MB).

The transport table is optional, it is for advanced users. It allows to forward mails for single users, whole domains or all mails to another server. For example,

domain

transport

example.com

smtp:[1.2.3.4]

would forward all emails for example.com via the smtp protocol to the server with the IP address 1.2.3.4 (the square brackets [] mean "do not make a lookup of the MX DNS record" (which makes sense for IP addresses...). If you use a fully qualified domain name (FQDN) instead you would not use the square brackets.).

BTW, (I'm assuming that the IP address of your mail server system is 192.168.0.100) you can access phpMyAdmin over http://192.168.0.100/phpmyadmin/ in a browser and log in as mail_admin. Then you can have a look at the database. Later on you can use phpMyAdmin to administrate your mail server.

5 Configure Postfix

Now we have to tell Postfix where it can find all the information in the database. Therefore we have to create six text files. You will notice that I tell Postfix to connect to MySQL on the IP address 127.0.0.1 instead of localhost. This is because Postfix is running in a chroot jail and does not have access to the MySQL socket which it would try to connect if I told Postfix to use localhost. If I use 127.0.0.1 Postfix uses TCP networking to connect to MySQL which is no problem even in a chroot jail (the alternative would be to move the MySQL socket into the chroot jail which causes some other problems).

Please make sure that /etc/mysql/my.cnf contains the following line:

vi /etc/mysql/my.cnf

[...]
# Instead of skip-networking the default is now to listen only on
# localhost which is more compatible and is not less secure.
bind-address = 127.0.0.1
[...]

If you had to modify /etc/mysql/my.cnf, please restart MySQL now:

/etc/init.d/mysql restart

Run

netstat -tap | grep mysql

to make sure that MySQL is listening on 127.0.0.1 (localhost.localdomain):

6 Configure Saslauthd

Then edit /etc/default/saslauthd. Set START to yes and change the line OPTIONS="-c -m /var/run/saslauthd" to OPTIONS="-c -m /var/spool/postfix/var/run/saslauthd -r":

vi /etc/default/saslauthd

#
# Settings for saslauthd daemon
# Please read /usr/share/doc/sasl2-bin/README.Debian for details.
#
# Should saslauthd run automatically on startup? (default: no)
START=yes
# Description of this saslauthd instance. Recommended.
# (suggestion: SASL Authentication Daemon)
DESC="SASL Authentication Daemon"
# Short name of this saslauthd instance. Strongly recommended.
# (suggestion: saslauthd)
NAME="saslauthd"
# Which authentication mechanisms should saslauthd use? (default: pam)
#
# Available options in this Debian package:
# getpwent -- use the getpwent() library function
# kerberos5 -- use Kerberos 5
# pam -- use PAM
# rimap -- use a remote IMAP server
# shadow -- use the local shadow password file
# sasldb -- use the local sasldb database file
# ldap -- use LDAP (configuration is in /etc/saslauthd.conf)
#
# Only one option may be used at a time. See the saslauthd man page
# for more information.
#
# Example: MECHANISMS="pam"
MECHANISMS="pam"
# Additional options for this mechanism. (default: none)
# See the saslauthd man page for information about mech-specific options.
MECH_OPTIONS=""
# How many saslauthd processes should we run? (default: 5)
# A value of 0 will fork a new process for each connection.
THREADS=5
# Other options (default: -c -m /var/run/saslauthd)
# Note: You MUST specify the -m option or saslauthd won't run!
#
# WARNING: DO NOT SPECIFY THE -d OPTION.
# The -d option will cause saslauthd to run in the foreground instead of as
# a daemon. This will PREVENT YOUR SYSTEM FROM BOOTING PROPERLY. If you wish
# to run saslauthd in debug mode, please run it by hand to be safe.
#
# See /usr/share/doc/sasl2-bin/README.Debian for Debian-specific information.
# See the saslauthd man page and the output of 'saslauthd -h' for general
# information about these options.
#
# Example for chroot Postfix users: "-c -m /var/spool/postfix/var/run/saslauthd"
# Example for non-chroot Postfix users: "-c -m /var/run/saslauthd"
#
# To know if your Postfix is running chroot, check /etc/postfix/master.cf.
# If it has the line "smtp inet n - y - - smtpd" or "smtp inet n - - - - smtpd"
# then your Postfix is running in a chroot.
# If it has the line "smtp inet n - n - - smtpd" then your Postfix is NOT
# running in a chroot.
#OPTIONS="-c -m /var/run/saslauthd"
OPTIONS="-c -m /var/spool/postfix/var/run/saslauthd -r"

Then create the file /etc/pam.d/smtp. It should contain only the following two lines (go sure to fill in your correct database details):

During the installation, the SSL certificates for IMAP-SSL and POP3-SSL are created with the hostname localhost. To change this to the correct hostname (server1.example.com in this tutorial), delete the certificates...

Afterwards we must configure amavisd-new. The configuration is split up in various files which reside in the /etc/amavis/conf.d directory. Take a look at each of them to become familiar with the configuration. Most settings are fine, however we must modify three files:

First we must enable ClamAV and SpamAssassin in /etc/amavis/conf.d/15-content_filter_mode by uncommenting the @bypass_virus_checks_maps and the @bypass_spam_checks_maps lines:

And then you should take a look at the spam settings and the actions for spam-/virus-mails in /etc/amavis/conf.d/20-debian_defaults. There's no need to change anything if the default settings are ok for you. The file contains many explanations so there's no need to explain the settings here:

Finally, edit /etc/amavis/conf.d/50-user and add the line $pax='pax'; in the middle:

vi /etc/amavis/conf.d/50-user

use strict;
#
# Place your configuration directives here. They will override those in
# earlier files.
#
# See /usr/share/doc/amavisd-new/ for documentation and examples of
# the directives you can use in this file
#
$pax='pax';
#------------ Do not modify anything below this line -------------
1; # ensure a defined return

Afterwards, run these commands to add the clamav user to the amavis group and to restart amavisd-new and ClamAV:

Over 8 years of experience as a Linux System Engineer. Srijan is an RHCE (Red Hat Certified Engineer) with in-depth knowledge in RHEL and CentOS, he also worked a lot with Debian and Ubuntu based systems, VM management and installing and maintaining hosting servers.

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Comments

Is it possible to set the virtual_mailbox_base parameter on a per domain basis? For example: I have example.org and a user called example. I would like to have the virtual_mailbox_base=/home/example/mail. Then I have another called sample.org with a user called sample. Likewise, I would like to have the virtual_mailbox_base=/home/sample/mail. Is this possible? I would rather not lump all of my virtual mailboxes in one location, /var/mail/vmail/<domain>